Mesmerizing Benthid

Hexproof on a five-mana body is usually the whole selling point, but here the keyword is conditional and self-supplied: control an Illusion and the Octopus cannot be targeted by your opponents, so the two 0/2 tokens that arrive alongside it are not just chump blockers, they are the license for the 4/5 to stay on the battlefield untouched. That knot is the design. An opponent who wants to remove the body has to clear both Illusions first, and the Illusions are miserable to attack into because each one that blocks strands the attacker: whatever crashed into the wall does not untap during its controller's next untap step, so the swing costs the attacker a full turn of that creature's availability on top of the failed trade. The tokens punish aggression twice, once as a wall and once as a lockdown on the thing that hit the wall. Structurally this is a tempo card wearing a control card's stat line. It does not close games quickly and it does not generate ongoing card advantage; what it does is make the ground a punishing place to trade creatures, then insulate its own threat from spot removal while it does. Answering the whole package (a resilient body plus two speed bumps that also freeze attackers) costs more resources than the five mana that assembled it, which is why a sweeper is the clean out: it never targets anything, so the hexproof clause never comes up.